Nathan Matthews, 28, told detectives after his arrest on suspicion of murdering his stepsister that he kept girlfriend Shauna Hoare, 21, in the dark over what had happened.

Shauna Hoare being interviewed by police

Matthews and Hoare had first been arrested on February 28 on suspicion of kidnapping Becky and were then arrested on March 2 on suspicion of her murder.

During the early hours of the following day police discovered 16-year-old Becky's remains in a garden shed at 9 Barton Court, Bristol - 80 metres from Matthews and Hoare's home at Cotton Mill Lane.

On March 4, Matthews, a former TA soldier turned Chinese takeaway delivery driver, gave police a prepared written statement.

He stated that if Hoare's DNA or fingerprints were found on anything to do with the dismembering of Becky's body into eight parts, there would be an "entirely innocent" explanation.

Matthews also insisted that Hoare would not have heard the attack on Becky at her home in Crown Hill, St George, Bristol, on February 19 and that he kept the teenager's body hidden from his girlfriend.

He said: "I Nathan Charles Matthews have the following comments to make.

"Further to my statement of March 2 2015 and in the light of disclosure handed to my solicitor by the police on the evening of March 3 2015.

"This disclosure is in the form of two sheets of printed information headed 'pre-interview disclosure 3 for Nathan Matthews' that is the fourth disclosure document given to my solicitor.

"Since my arrest I have made it clear I have difficulty remembering what happened on which day.

"So when I said in my statement of March 2 that I thought I had left Shauna at my mother's house on the Saturday I accept now his must have been Friday February 20.

"I did go shopping with Shauna on the Sunday but she did not know why I bought the items from Wilkinson and the 99p store.

"I did not tell her the real reason for buying them.

"I cannot remember if she asked why I was buying them but if she did I would have lied.

"If Shauna's fingerprints or DNA are on any of the things I used when dealing with the body it will be entirely innocent.

"For example Shauna may have helped unpack the shopping.

"I do not believe Shauna could have heard any of the struggle between me and Rebecca Watts at 18 Crown Hill.

"At all times I kept the body hidden from Shauna.

"I have now also seen a fifth disclosure document consisting of two printed pages and labelled 'pre-interview disclosure notice 4' which was handed to my solicitor this morning.

"I have no further comment to make."

Matthews, of Hazelbury Drive, Warmley, South Gloucestershire, denies murder and conspiracy to kidnap.

He admits killing Becky, perverting the course of justice, preventing the burial of a corpse and possessing a prohibited weapon.

Hoare, of Cotton Mill Lane, Bristol, denies murder, conspiracy to kidnap, perverting the course of justice, preventing burial of a corpse and possessing a prohibited weapon.

The residents of the Barton Court property, Karl Demetrius, 30, and his partner Jaydene Parsons, 23, admit assisting an offender.

The jury later watched an interview filmed by police with Matthews on March 3 after Becky's body parts had been found.

Matthews - who was sat in a chair behind a table, frequently kept his head in his hands and sobbed - told detectives: "Obviously I came up with the idea to scare her to try and basically make her more appreciative of life so she would be more appreciative for other people.

"She would be grateful that she wasn't harmed or anything like that.

"Obviously she would leave things on the floor for Mum to trip over and talk to her - like nasty comments and talk to her like dirt on the floor.

"It was to scare her and obviously after she had been released when she got back she obviously would have been scared and appreciative of things as people are.

"Obviously I would put her in the suitcase, obviously put tape round her mouth so she couldn't make a noise then once I got her in the car I would say something to Shauna that I had to go out for some reason, I'd make up an excuse.

"I was thinking of a wooded area but obviously take her back out, obviously still have the mask on and obviously scare her and say something along the lines 'start treating people better and not being a bitch and self-centred' and say 'or it will get worst'.

"Obviously I hadn't figured out exactly how to walk away after.

"I don't know if she would have followed but she wouldn't have followed because I have a feeling you wouldn't follow someone that has done that.

"I would have chucked everything and gone back and acted as normal, gone back to my Mum's and acted as normal.

"She wouldn't listen to me about leaving shit on the floor for my Mum to trip up on, she wouldn't listen to her Dad.